Nutrition FN 225
Carbohydrates

Introduction to Carbohydrates

If someone says to you, "I love carbohydrates, and I eat them all day long!" what would you assume they're eating?

Do you picture this?

Fig. 1.1. Examples of carbohydrate-rich snack foods.

And this?

Fig. 1.2. Examples of grain-based foods.

When we ask this question in class, most students describe foods like the ones above. However, carbohydrates are found not just in grains, or in sweets and processed foods, but in every food group. In fact, carbohydrates are the most abundant nutrient (except water) in the diets of most humans around the world. Since the dawn of agriculture, human cultures have relied on staple grains, such as corn, rice, and wheat, as the foundation of their diets, and these foods are rich in carbohydrates. But fruits and vegetables, dairy products, legumes, and nuts also have naturally-occurring carbohydrates. And of course, carbohydrates are a key ingredient in desserts, sugar-sweetened beverages like sodas, and many of the packaged snack foods that are readily available and -- let's face it -- can be hard to stop eating. In other words, if someone says they eat a high carbohydrate diet, that could mean many different things. They very well could be talking about a balanced diet focused on whole foods, like this:

Fig. 2.3. Examples of whole foods containing carbohydrates, including fresh fruit, legumes and grains, and cheese.

The diet industry likes to sell us simple messages about "good" and "bad" foods, and these days, we tend to hear that carbohydrates are in the "bad" group. But given that carbohydrates are in so many different types of foods, that's obviously an oversimplified message -- and it's not fair to all of the awesome sources of carbohydrates in the world of food. Not all carbohydrate-rich foods are the same. In this unit, you'll learn to appreciate the nutrient-dense carbohydrate foods, identify which don't offer as valuable a nutritional package, and understand how a balanced diet can include all of them.

Topics Covered in this Unit

1. Types of carbohydrates

2. Food sources of carbohydrates and guidelines for intake

3. Digestion and absorption of carbohydrates

4. Glucose utilization and regulation in the body

5. Fiber: Benefits, recommendations, food sources, and whole vs. refined grains

6. Sugar: Food sources, health Implications, intakes, and label-reading to identify sugar

7. Sugar substitutes

Course Learning Outcomes Covered

1. Define and classify the six classes of nutrients.

2. Identify where the six classes of nutrients are found in foods.

3. Explain how the six classes of nutrients are digested, absorbed, metabolized, and utilized.

4. Distinguish between adequate nutrient intake, deficiencies, and toxicities and how these levels impact body systems and health outcomes.

5. Acknowledge the importance of a moderate approach when it comes to nutrition and weight management, recognizing all foods can fit into a healthful diet.

6. Critically evaluate and compare nutrition labels and determine the nutrient density of each food.

Image Credits

1. Potato chips picture by Kate Ter Haar, CC BY 2.0, http://flic.kr/p/FCeWmT; M&Ms picture by Wade Brooks, CC BY-NC 2.0,  http://flic.kr/p/jkJZgr; Pecan pastry picture by Artizone, CC BY-NC-ND 2.0, http://flic.kr/p/8Lwo4z.

2. Bread picture by David Stewart, CC BY 2.0,  http://flic.kr/p/27Hosch; Pasta picture by Yasumari SASAKI, CC BY 2.0, http://flic.kr/p/2GE3in; Rice photo by Francesca Nocella, CC BY-SA 2.0, https://flic.kr/p/4FGodR.

3. Fruit picture by Allen Gottfried, CC BY-SA 2.0, http://flic.kr/p/ngSWG5;  Beans and grain picture by Evans E, CC BY 2.0,  http://flic.kr/p/dRrZ4R; Cheese picture by Finite Focus, CC BY-NC 2.0, http://flic.kr/p/5HoGS9.

To get started, scroll down and click next page or cklick "types" in the navigation above.

Types of Carbohydrates

On this page, we'll get acquainted with the chemical structure of different types of carbohydrates and learn where we find them in foods.

First, all carbohydrates are made up of the same chemical elements:

• carbon (that's the "carbo-" part)

• hydrogen and oxygen, in about a two-to-one proportion, just like in H2O (that's the "-hydrate" part)

For this reason, you may see carbohydrates abbreviated as "CHO" in our class.

Carbohydrates can be divided into two main types: simple and complex. Simple carbohydrates are made up of just one or two sugar units, whereas complex carbohydrates are made up of many sugar units. We'll look at each of these in turn. This figure gives you an overview of the types of carbohydrates that we'll cover.

Fig. 2.1. Carbohydrates can be divided into two main types: simple (including monosaccharides and disaccharides) and complex.

Simple carbohydrates

Simple carbohydrates are sometimes called "sugars" or "simple sugars." There are 2 types of simple carbohydrates: monosaccharides and disaccharides.

Monosaccharides contain just one sugar unit, so they're the smallest of the carbohydrates. (The prefix "mono-" means "one.") The small size of monosaccharides gives them a special role in digestion and metabolism. Food carbohydrates have to be broken down to monosaccharides before they can be absorbed in the gastrointestinal tract, and they also circulate in blood in monosaccharide form.

There are 3 monosaccharides:

1. Glucose

2. Fructose

3. Galactose

Note that all three have the same chemical formula (C6H12O6); the atoms are just arranged a bit differently.

1 - Glucose

Here's the chemical structure of glucose:

In this class, we'll sometimes use a simpler green hexagon to represent glucose:

You're already familiar with glucose, because it's the main product of photosynthesis. Plants make glucose as a way of storing the sun's energy in a form that it can use for growth and reproduction.

In humans, glucose is one of the most important nutrients for fueling the body. It's especially important for the brain and nervous system, which aren't very good at using other fuel sources. Muscles, on the other hand, can use fat as an energy source. (In practice, your muscles are usually using some combination of fat and glucose for energy, which we'll learn more about later.)

Food sources of glucose: Glucose is found in fruits and vegetables, as well as honey, corn syrup, and high fructose corn syrup. (All plants make glucose, but much of the glucose is used to make starch, fiber, and other nutrients. The foods listed here have glucose in its monosaccharide form.)

2 - Fructose

Here's the chemical structure of fructose:

In this class, we'll sometimes use a simpler purple pentagon to represent fructose:

Fructose is special because it is the sweetest carbohydrate. Plants make a lot of fructose as a way of attracting insects and animals, which help plants to reproduce. For example, plants make nectar, which is high in fructose and very sweet, to attract insects that will pollinate it. Plants also put fructose into fruit to make it tastier. Animals eat the fruit, wander away, and later poop out the seeds from the fruit, thereby sowing the seeds of the next generation. Animal gets a meal, and the plant gets to reproduce: win-win!

Fig. 2.2. Fructose in nature: A bee collects sweet nectar from a flower, in the process spreading pollen from flower to flower and helping plants to reproduce. Bees use nectar to make honey, which humans harvest for use as a sweetener. (Honey contains a mix of sucrose, fructose, and glucose). A kiwi is sweetened in part by fructose. Animals enjoy the sweet fruit and then later poop out the seeds, sowing them for a new generation of kiwi trees.

Food sources of fructose: Fruits, vegetables, honey, high fructose corn syrup

3 - Galactose

Here is the chemical structure of galactose:

In this class, we'll sometimes use a blue hexagon to represent galactose:

Food sources of galactose: Galactose is found in milk (and dairy products made from milk), but it's almost always linked to glucose to form a disaccharide (more on that in a minute). We rarely find it in our food supply in monosaccharide form.

The second type of simple carbohydrates is disaccharides. They contain two sugar units bonded together.

There are 3 disaccharides:

1. Maltose (glucose + glucose)

2. Sucrose (glucose + fructose)

3. Lactose (glucose + galactose)

1 - Maltose

Maltose is made of two glucose molecules bonded together. It doesn't occur naturally in any appreciable amount in foods, with one exception: sprouted grains. Grains contain a lot of starch, which is made of long chains of glucose (more on this in a minute), and when the seed of a grain starts to sprout, it begins to break down that starch, creating maltose. If bread is made from those sprouted grains, that bread will have some maltose. Sprouted grain bread is usually a little heavier and sweeter than bread made from regular flour.

Maltose also plays a role in the production of beer and liquor, because this process involves the fermentation of grains or other carbohydrate sources. Maltose is formed during the breakdown of those carbohydrates, but there is very little remaining once the fermentation process is complete.

You can taste the sweetness of maltose if you hold a starchy food in your mouth for a minute or so. Try this with a simple food like a soda cracker. Starch is not sweet, but as the starch in the cracker begins to break down with the action of salivary amylase, maltose will form, and you'll taste the sweetness!

2 - Sucrose

Sucrose is made of a glucose molecule bonded to a fructose molecule. It's made by plants for the same reason as fructose -- to attract animals to eat it and thereby spread the seeds.

Sucrose is naturally-occurring in fruits and vegetables. (Most fruits and vegetables contain a mixture of glucose, fructose, and sucrose.) But humans have also figured out how to concentrate the sucrose in plants (usually sugar cane or sugar beets) to make refined table sugar. We also find sucrose in maple syrup and honey.

The sucrose found in sweet potato is chemically identical to the sucrose found in table sugar. Likewise, the fructose found in a fig is chemically identical to the fructose found in high fructose corn syrup. As we'll discuss more later, what's different is the package the sugars come in. When you eat a sweet potato or a fig, you also get lots of fiber, vitamins, and minerals in that package, whereas sugar and high fructose corn syrup only provide sugar, nothing else. It's not a bad thing to eat sugar. After all, it's a vital fuel for our brain and nervous system. But paying attention to the package it comes in can help us make good overall choices for health.  

3 - Lactose

Lactose is made of a glucose molecule bonded to a galactose molecule. It is sometimes called "milk sugar" as it is found in dairy products like milk, yogurt, and cheese. These are the only animal foods that have significant amounts of carbohydrate. Most of our carbohydrates come from plant foods.

Complex carbohydrates

Complex carbohydrates are also called polysaccharides, because they contain many sugars. (The prefix "poly-" means "many.") There are 3 main polysaccharides:

1. Starch

2. Glycogen

3. Fiber

All three of these polysaccharides are made up of many glucose molecules bonded together, but they differ in their structure and the type of bonds.

1 - Starch

Starch is made up of long chains of glucose. If these chains are straight, they're called amylose; if they're branched, they're called amylopectin.

Here is an amylose segment containing 3 glucose units.

The next figure shows an amylopectin segment containing 4 glucose units. The chemical structure is represented differently, but can you spot the place where it branches?

Using our green hexagon to represent glucose, you can picture starch as something like this:

Humans have digestive enzymes to break down both types of starch, which we'll discuss on the next page.

Starch is the storage form of carbohydrate in plants. Plants make starch in order to store glucose. For example, starch is in seeds to give the seedling energy to sprout, and we eat those seeds in the form of grains, legumes (soybeans, lentils, pinto and kidney beans, for example), nuts, and seeds. Starch is also stored in roots and tubers to provide stored energy for the plant to grow and reproduce, and we eat these in the form of potatoes, sweet potatoes, carrots, beets, and turnips.

When we eat plant foods with starch, we can break it down into glucose to provide fuel for our body's cells. In addition, starch from whole plant foods comes packaged with other valuable nutrients. We also find refined starch - such as corn starch - as an ingredient in many processed foods, because it serves as a good thickener.

2 - Glycogen

Glycogen is structurally similar to amylopectin, but it's the storage form of carbohydrate in animals, humans included. It's made up of highly branched chains of glucose, and it's stored in the liver and skeletal muscle. The branched structure of glycogen makes it easier to break down quickly to release glucose to serve as fuel when needed on short notice.

Liver glycogen is broken down to glucose, which is released into the bloodstream and can be used by cells around the body. Muscle glycogen provides energy only for muscle, to fuel activity. That can come in handy if you're being chased by a lion, or sprinting to make your bus!

Even though glycogen is stored in the liver and muscles of animals, we don't find it in meat, because it's broken down soon after slaughter. Thus, glycogen is not found in our food. Instead, we have to make it in our liver and muscle from glucose.

Here's a beautiful depiction of glycogen.

Fig. 2.3 - Glycogen is made from long, branching chains of glucose, radiating around a central protein.

3 - Fiber

Fiber includes carbohydrates and other structural substances in plants that are indigestible to human enzymes. Fiber is made by plants to provide protection and structural support. Think about thick stems that help a plant stand upright, tough seed husks, and fruit skin that protect what's growing inside. These are full of fiber.

Fig. 2.4 - Examples of food plants high in fiber, including wheat, broccoli, and apples.

In our food, we find fiber in whole plant foods like whole grains, seeds, nuts, fruits, vegetables, and legumes.

One of the most common types of fiber is cellulose, the main component in plant cell walls. The chemical structure of cellulose is shown in the figure below, with our simplified depiction next to it. You can see that cellulose has long chains of glucose, similar to starch, but they're stacked up, and there are hydrogen bonds linking the stacks.

When we eat fiber, it passes through the small intestine intact, because we don't have digestive enzymes to break it down. Then, in the large intestine, our friendly microbiota -- the bacteria that live in our colons -- go to work on the fiber. Some fiber can be fermented by those bacteria. We'll discuss fiber more later in the unit.

Self-Check

References

1. Levin, R.J. Carbohydrates. In: Modern Nutrition in Health and Disease, 9th Ed., Baltimore, MD, Lippincott Williams and Wilkins, 1999

2. US Department of Agriculture (USDA), Agricultural Research Service, Nutrient Data Laboratory. USDA National Nutrient Database for Standard Reference, Legacy. Version Current: April 2018. Internet: http://www.ars.usda.gov/nutrientdata

Image Credits

1. Fig. 2.1 - Types of carbohydrates diagram by Alice Callahan made with Microsoft SmartArt, CC BY-SA 4.0

2. Chemical structures of glucose, fructose, galactose, amylose, amylopectin are public domain, accessed from Wikipedia

3. Simple carbohydrate diagrams (with hexagons, pentagon) by Alice Callahan, CC BY-SA 4.0

4. Fig. 2.2 - Flower with bee image by pontla, https://flic.kr/p/25uiqgH; Honey image by sunny mama, https://flic.kr/p/rx1Vam; Kiwi image by ereta ekarafi, https://flic.kr/p/9ENG11, all CC BY-NC-ND 2.0

5. Fig. 2.3 - Glycogen image by Häggström, Mikael (2014). "Medical gallery of Mikael Häggström 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.008. ISSN 2002-4436. Public Domain.

6. Fig. 2.4 - Wheat image by Bernat Caser, https://flic.kr/p/2df9Da; Broccoli image by albedo20, https://flic.kr/p/5hWGB9; Apple - Fiona Shields, https://flic.kr/p/5dUC8m, all CC BY-NC-ND 2.0

7. Chemical structure of cellulose by laghi.l, CC BY-SA 3.0

Carbohydrate Food Sources and Guidelines for Intake

Where do we find carbohydrates in foods?

Looking at the food groups represented in MyPlate below, which food groups do you think contain carbohydrates? If you answered, all of them, you're correct! This section will review which food groups contain the different types of carbohydrates. One of the goals of this course is to learn more about the different nutrients in foods and to understand the importance of eating a wide variety of foods from the different food groups.

Figure 3.1 - Choose MyPlate graphic illustrating the USDA food groups: fruits, vegetables, grains, protein and dairy.

Fruits- Fruits are sweet, so we know they must contain sugar. Fruits contain sucrose, glucose, and fructose. This sugar is naturally-occurring and comes packaged with other great nutrients, like Vitamin C and potassium. Whole fruit also contains fiber, since fiber is found in all whole plant foods. Juice has little to no fiber, even high pulp orange juice.

Vegetables- Some vegetables are sweet and also contain sugar, although much less than fruit. Similar to fruits, some vegetables (like carrots and green beans) contain small amounts of sucrose, glucose, and fructose. Starchy vegetables (corn, peas, and potatoes, for example) primarily contain starch but some are also sweet and contain sucrose, glucose, and fructose (sweet potatoes and sweet corn, for example). Just like whole fruit, any whole vegetable also contains fiber.  

Dairy- This is the one animal food that contains carbohydrate. Milk, cheese, and yogurt contain naturally-occurring lactose. If dairy (like yogurt) is sweetened, then it will also contain added sugar like sucrose (white cane sugar) or fructose and glucose (honey and/or HFCS).

Grains- Grains naturally contain starch and fiber. Sprouted grains also contain maltose. If grains are sweetened (sugar is added), they might contain  sucrose (white cane sugar) or fructose and glucose (honey and/or HFCS).

Protein- Meats do not contain carbohydrate, but many plant foods that fall into the protein group, like beans and nuts, contain starch and fiber.  

Fats- Concentrated fats like butter and oil do not contain carbohydrate.

This information is summarized in the table below:

Table 3.1 USDA food groups with examples of foods and type of carbohydrate present within each food group.

Looking at all the foods that contain carbohydrates, you might be able to guess why eliminating carbohydrates from the diet can lead to weight loss. It drastically reduces the variety of choices one has, leaving you primarily with low carbohydrate veggies and meats. Not surprisingly, people usually consume less calories with this way of eating.  However, for most people, this is not a sustainable or enjoyable way of eating, and it can also be hard to consume a nutritionally balanced diet with so many foods off-limits.

Carbohydrate Guidelines for Intake

Total Carbohydrate Intake

The recommended dietary allowance (RDA) for total carbohydrate intake is 130 grams. This is the minimum amount of glucose utilized by the brain, so if you consume less than this, you will probably go into ketosis. In order to meet the body's high energy demand for glucose, the acceptable macronutrient distribution range (AMDR) for an adult is 45%-65% of total calories. This is about 225 grams to 325 grams of carbohydrate per day if eating a 2,000 Calorie diet. (REMEMBER: 1 gram of carbohydrate contains 4 Calories.)

Fiber Intake

The Adequate Intake (AI) for fiber is 14 grams of fiber for every 1,000 Calories consumed. This is about 28 grams for an adult female (19-30 years old) and 38 grams for an adult male (19-30 years old). Most people in the United States only get half the amount of fiber they need in a day -- about 12 to 18 grams.

Added Sugar Intake

The 2015 dietary guidelines recommend that less than 10% of total Calories come from added sugars because of its link to obesity and chronic disease. This means that someone eating a 2,000 Calorie diet would want to limit their added sugar intake to about 12 teaspoons per day. To put that in perspective, a 12 oz can of soda has about 10 teaspoons of sugar. We will discuss added sugar in more detail later in the lesson.

Below is a chart summarizing the above recommendations.

Table 3.2 Dietary Recommendations for Carbohydrates

Self Check

Resources

1. US Department of Health and Human Services and U.S. Department of Agriculture. 2015. Dietary Guidelines for Americans. https://health.gov/dietaryguidelines/2015/guidelines/

2. Institute of Medicine, Food and Nutrition Board, 2005. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, DC; The National Academy of Sciences.

Image Credits

1. MyPlate image from https://www.choosemyplate.gov/myplate-graphic-resources, public domain.

Digestion and Absorption of Carbohydrates

Imagine taking a bite of pizza. It tastes amazing, but it's also full of fuel for your body, much of it in the form of carbohydrates.

What types of carbohydrates would you find in that bite?

• Lactose from the cheese

• Sucrose, glucose, and fructose from the naturally-occurring sugars in the tomatoes, as well as sugar that may have been added to the sauce

• Starch in the flour used to make the crust

• Fiber in the flour, tomatoes, and basil.

In order to use these food carbohydrates in your body, you first need to digest them. Last week, we explored the gastrointestinal system and the basic process of digestion. Now that you know about the different types of carbohydrates, we'll take a closer look at how these molecules are digested as they travel through the GI system.

In the image below, follow the numbers to see what happens to carbohydrates at each site of digestion.

Fig. 4.1. The digestive system

1 - Mouth or Oral Cavity

As you chew your bite of pizza, you're using mechanical digestion to begin to break it into smaller pieces and mix it with saliva, produced by several salivary glands in the oral cavity.

Some enzymatic digestion of starch occurs in the mouth, due to the action of the enzyme salivary amylase. This enzyme starts to break the long glucose chains of starch into shorter chains, some as small as maltose. (The other carbohydrates in the bread don't undergo any enzymatic digestion in the mouth.)

Fig. 4.2. The enzyme salivary amylase breaks starch into smaller polysaccharides and maltose.

2 - Stomach

The low pH in the stomach inactivates salivary amylase, so it no longer works once it arrives at the stomach. Although there's more mechanical digestion in the stomach, there's little chemical digestion of carbohydrates here.

3 - Small intestine

Most carbohydrate digestion occurs in the small intestine, thanks to a suite of enzymes. Pancreatic amylase is secreted from the pancreas into the small intestine, and like salivary amylase, it breaks starch down to small oligosaccharides (containing 3 to 10 glucose molecules) and maltose.

Fig. 4.3. The enzyme pancreatic amylase breaks starch into smaller polysaccharides and maltose.

The rest of the work of carbohydrate digestion is done by enzymes produced by the enterocytes, the cells lining the small intestine. When it comes to digesting your slice of pizza, these enzymes will break down the maltase formed in the process of starch digestion, the lactose from the cheese, and the sucrose present in the sauce.

• Maltose is digested by maltase, forming 2 glucose molecules

• Lactose is digested by lactase, forming glucose and galactose

• Sucrose is digested by sucrase, forming glucose and fructose

Fig. 4.4. Action of the enzymes maltase, lactase, and sucrase.

(Recall that if a person is lactose intolerant, they don't make enough lactase enzyme to digest lactose adequately. Therefore, lactose passes to the large intestine. There it draws water in by osmosis and is fermented by bacteria, causing symptoms such as flatulence, bloating, and diarrhea.)

By the end of this process of enzymatic digestion, we're left with three monosaccharides: glucose, fructose, and galactose. These can now be absorbed across the enterocytes of the small intestine and into the bloodstream to be transported to the liver.

Digestion and absorption of carbohydrates in the small intestine are depicted in a very simplified schematic below. (Remember that the inner wall of the small intestine is actually composed of large circular folds, lined with many villi, the surface of which are made up of microvilli. All of this gives the small intestine a huge surface area for absorption.)

Fig. 4.5. Digestion and absorption of carbohydrates in the small intestine.

Fructose and galactose are converted to glucose in the liver. Once absorbed carbohydrates pass through the liver, glucose is the main form of carbohydrate circulating in the bloodstream.

4 - Large Intestine or Colon

Any carbohydrates that weren't digested in the small intestine -- mainly fiber -- pass into the large intestine, but there's no enzymatic digestion of these carbohydrates here. Instead, bacteria living in the large intestine, sometimes called our gut microbiota, ferment these carbohydrates to feed themselves. Fermentation causes gas production, and that's why we may experience bloating and flatulence after a particularly fibrous meal. Fermentation also produces short-chain fatty acids, which our large intestine cells can use as an energy source. Over the last decade or so, more and more research has shown that our gut microbiota are incredibly important to our health, playing important roles in the function of our immune response, nutrition, and risk of disease. A diet high in whole food sources of fiber helps to maintain a population of healthy gut microbes.

Summary of Carbohydrate Digestion:

The primary goal of carbohydrate digestion is to break polysaccharides and disaccharides into monosaccharides, which can be absorbed into the bloodstream.   

1. After eating, nothing needs to happen in the digestive tract to the monosaccharides in a food like grapes, because they are already small enough to be absorbed as is.  

2. Disaccharides in that grape or in a food like milk are broken down (enzymatically digested) in the digestive tract to monosaccharides (glucose, galactose, and fructose).   

3. Starch in food is broken down (enzymatically digested) in the digestive tract to glucose molecules.  

4. Fiber in food is not enzymatically digested in the digestive tract, because humans don't have enzymes to do this. However, some dietary fiber is fermented in the large intestine by gut microbes.

Table 4.1. Summary of Enzymatic Digestion of Carbohydrate

This video reviews the process of carbohydrate digestion: https://www.wiley.com/college/grosvenor/0470197587/animations/dig3a/

This video will help you identify carbohydrates in foods, what carbohydrates need to be enzymatically digested, and what is absorbed: https://youtu.be/XcIInk32nn4

Self Check

References

1. Klein, S., Cohn, S.M., Alpers, D.H., The Alimentary Tract in Nutrition, In: Modern Nutrition in Health and Disease, 9th Ed., Baltimore, MD, Lippincott Williams and Wilkins, 1999

2. Harvard T. H. Chan School of Public Health, "The Microbiome," https://www.hsph.harvard.edu/nutritionsource/microbiome/, accessed September 10, 2018

Image Credits

1. Eating pizza photo by @mark-c from nappy.co, CC0

2. Digestive system image by Mariana Ruiz, public domain, edited by Alice Callahan

3. Carbohydrate digestion schematics by Alice Callahan, CC BY-NC-SA 4.0

4. Carbohydrate absorption image Alice Callahan, CC BY-NC-SA 4.0

5. Carbohydrate and digestion summary chart by Tamberly Powell, CC BY-NC-SA 4.0

Glucose Regulation and Utilization in the Body

On the last page, we traced the process of digesting the carbohydrates in a slice of pizza through the gastrointestinal tract, ending up with the absorption of monosaccharides across the cells of the small intestine and into the bloodstream. From there, they travel to the liver, where fructose and galactose are converted to glucose.

After any meal containing carbohydrates, you experience a rise in blood glucose that can serve as fuel for cells around the body. But during the periods between meals, including while you're sleeping and exercising, your body needs fuel, too. To ensure that you have enough glucose in your blood at any given time, your body has a finely-tuned system to regulate your blood glucose concentration. This system allows you to store glucose when you have excess available (when your blood glucose is high) and to pull glucose out from your stores when needed (when your blood supply gets low).

Your body's ability to maintain equilibrium or a steady state in your blood glucose concentration is called homeostasis. It's a critical part of normal physiology, because if your blood glucose gets too low (called hypoglycemia), cellular function starts to fail, especially in the brain. If blood glucose gets too high (called hyperglycemia), it can cause damage to cells.

Hormones Involved in Blood Glucose Regulation

Central to maintaining blood glucose homeostasis are two hormones, insulin and glucagon, both produced by the pancreas and released into the bloodstream in response to changes in blood glucose.

• Insulin is made by the beta-cells of the pancreas and released when blood glucose is high. It causes cells around the body to take up glucose from the blood, resulting in lowering blood glucose concentrations.

• Glucagon is made by the alpha-cells of the pancreas and released when blood glucose is low. It causes glycogen in the liver to break down, releasing glucose into the blood, resulting in raising blood glucose concentrations. (Remember that glycogen is the storage form of glucose in animals.)

The image below depicts a mouse islet of Langerhans, a cluster of endocrine cells in the pancreas. The beta-cells of the islet produce insulin, and the alpha-cells produce glucagon.

Fig. 5.1. A mouse islet of Langerhans, visualized with immunofluorescent microscopy. In this image, cell nuclei are stained blue, insulin is stained red, and blood vessels are stained green. You can see that this islet is packed with insulin and sits right next to a blood vessel, so that it can secrete the two hormones, insulin and glucagon, into the blood. Glucagon is not stained in this image, but it's there!

In the figure below, you can see blood glucose and insulin throughout a 24-hour period, including three meals. You can see that when glucose rises, it is followed immediately by a rise in insulin, and glucose soon drops again. The figure also shows the difference between consuming a sucrose-rich food and a starch-rich food. The sucrose-rich food results in a greater spike in both glucose and insulin. Because more insulin is required to handle that spike, it also causes a more precipitous decline in blood glucose. This is why eating a lot of sugar all at once may increase energy in the short-term, but soon after may make you feel like taking a nap!

Fig. 5.2. Typical pattern of blood glucose and insulin during a 24-hour period, showing peaks for each of 3 meals and highlighting the effects of consumption of sugar-rich foods.

Let's look a little closer at how insulin works, illustrated in the figure below. Insulin is released by the pancreas into the bloodstream. Cells around the body have receptors for insulin on their cell membranes. Insulin fits into its receptors (labeled as step 1 in the figure), kind of like a key in a lock, and through a series of reactions (step 2), triggers glucose transporters to open on the surface of the cell (step 3). Now glucose can enter the cell, making it available for the cell to use and at the same time lowering the concentration of glucose in the blood.

Fig. 5.3. Insulin binds to its receptors on the cell membrane, triggering GLUT-4 glucose transporters to open on the membrane. This allows glucose to enter the cell, where it can be used in several ways.

The figure also shows several different ways glucose can be used once it enters the cell.

• If the cell needs energy right away, it can metabolize glucose through cellular respiration, producing ATP (step 5).

• If the cell doesn't need energy right away, glucose can be converted to other forms for storage. If it's a liver or muscle cell, it can be converted to glycogen (step 4). Alternatively, it can be converted to fat and stored in that form (step 6).

In addition to its role in glucose uptake into cells, insulin also stimulates glycogen and fat synthesis as described above. It also stimulates protein synthesis. You can think of its role as signaling to the body that there's lots of energy around, and it's time to use it and store it in other forms.

On the other hand, when blood glucose falls, several things happen to restore homeostasis.

1. You receive messages from your brain and nervous system that you should eat. If that doesn't work, or doesn't work fast enough….

2. Glucagon is released from the pancreas into the bloodstream. In liver cells, it stimulates the breakdown of glycogen, releasing glucose into the blood.

3. In addition, glucagon stimulates a process called gluconeogenesis, in which new glucose is made from amino acids (building blocks of protein) in the liver and kidneys, also contributing to raising blood glucose.

How Glucose Provides Energy

Now let's zoom in on how exactly glucose provides energy to the cell. We can trace this process in the figure below.

Fig. 5.4. Overview of glucose metabolism in the fed state, when there is adequate glucose available. Glucose can be used to generate ATP for energy, or it can be stored in the form of glycogen or converted to fat for storage in adipose tissue.

1. Glucose, a 6-carbon molecule, is broken down to two 3-carbon molecules called pyruvate through a process called glycolysis.

2. Pyruvate enters a mitochondrion of the cell, where it is converted to a molecule called acetyl CoA.

3. Acetyl CoA goes through a series of reactions called the Krebs cycle. This cycle requires oxygen and produces carbon dioxide. It also produces several important high energy electron carriers called NADH2 and FADH2.

4. These high energy electron carriers go through the electron transport chain to produce ATP -- energy for the cell!

5. Note that the figure also shows that glucose can be used to synthesize glycogen or fat, if the cell already has enough energy.

What Happens When There Isn't Enough Glucose?

We've already talked about what happens when blood glucose falls: glucagon is released, and that stimulates the breakdown of glycogen as well as the process of gluconeogenesis from amino acids. These are important mechanisms for maintaining blood glucose levels to fuel the brain when carbohydrate is limited. Hypoglycemia (low blood glucose) can cause you to feel confused, shaky, and irritable, because your brain doesn't have enough glucose. If it persists, it can cause seizures and eventually coma, so it's good we have these normal mechanisms to maintain blood glucose homeostasis!

What happens if your carbohydrate supply is limited for a long time? This might happen if a person is starving or consuming a very low carbohydrate diet. In this case, your glycogen supplies will become depleted. How will you get enough glucose (especially for the brain) and energy? You'll have to use the other two macronutrients in the following ways:

1. Protein -- You'll continue to use some amino acids to make glucose through gluconeogenesis and others as a source of energy through acetyl CoA. However, if a person is starving, they also won't have extra dietary protein. Therefore, they start breaking down body proteins, which will cause muscle wasting.

2. Fat -- You can break down fat as a source of energy, but you can't use it to make glucose. Fatty acids can be broken down to acetyl CoA in the liver, but acetyl CoA can't be converted to pyruvate and go through gluconeogenesis. It can go through the Krebs cycle to produce ATP, but if carbohydrate is limited, the Krebs cycle gets overwhelmed. In this case, acetyl CoA is converted to compounds called ketones or ketone bodies. These can then be exported to other cells in the body, especially brain and muscle cells.

These pathways are shown in the figure below:

Fig. 5.5. During starvation or when consuming a low-carbohydrate diet, protein (amino acids) can be used to make glucose by gluconeogenesis, and fats can be used to make ketones in the liver. The brain can adapt to using ketones as an energy source in order to conserve protein and prevent muscle wasting.

Ketone production is important, because ketones can be used by tissues of the body as a source of energy during starvation or a low carbohydrate diet. Even the brain can adapt to using ketones as a source of fuel after about three days of starvation or very low carbohydrate diet. This also helps to preserve the protein in the muscle.

Ketones can be excreted in urine, but if ketone production is very high, they begin to accumulate in the blood, a condition called ketosis. Symptoms of ketosis include sweet-smelling breath, dry mouth, and reduced appetite. People consuming a very low carbohydrate diet may be in ketosis, and in fact, this is a goal of the currently popular ketogenic diet. (Ketones are acidic, so severe ketosis can cause the blood to become too acidic, a condition called ketoacidosis. This mainly happens with uncontrolled diabetes.)

Is following a ketogenic diet an effective way to lose weight? It can be, but the same can be said of any diet that severely restricts the types of foods that you're allowed to eat. Following a ketogenic diet means eating a high fat diet with very little carbohydrate and moderate protein. This means eating lots of meat, fish, eggs, cheese, butter, oils, and low carbohydrate vegetables, and eliminating grain products, beans, and even fruit. With so many fewer choices, you're likely to spend more time planning meals and less time mindlessly snacking. Being in ketosis also seems to reduce appetite, and it causes you to lose a lot of water weight initially. However, studies show that being in ketosis doesn't seem to increase fat-burning or metabolic rate. There are also concerns that the high levels of saturated fat in most ketogenic diets could increase risk of heart disease in the long term.  Finally, it's a very difficult diet to maintain for most people, and reverting back to your previous dietary patterns usually means the weight will come back. The ketogenic diet is also very similar to the Atkins diet that was all the rage in the 1990's, and we tend to be skeptical of such fad diets, preferring to focus instead on balance, moderation, and enjoyment of a wide variety of foods.

The following video reviews the concepts just covered: Glucose Regulation and Utilization in the Body

Diabetes

Diabetes is a chronic disease in which your normal system of regulating blood glucose doesn't work. There are three main types of diabetes: type 1, type 2, and gestational diabetes.

Type 1 Diabetes:

This is an autoimmune disease in which the beta-cells of the pancreas are destroyed by your own immune system. Without the beta-cells, you can't make enough insulin, so in type 1 diabetes, you simply don't have enough insulin to regulate your blood glucose levels. Remember how we said insulin is like the key that lets glucose into the body's cells? In type 1 diabetes, you're missing the key, so glucose stays in the blood and can't get into cells.

Fig. 5.6. In type 1 diabetes, the pancreas does not make enough insulin, so glucose transporters (GLUT-4) do not open on the cell membrane, and glucose is stuck outside the cell.

Common symptoms include weight loss and fatigue, because the body's cells are starved of glucose. Excess glucose from the blood is also excreted in the urine, increasing urination and thirst.

Once diagnosed, type 1 diabetics have to take insulin in order to regulate their blood glucose. Traditionally, this has required insulin injections timed with meals. New devices like continuous glucose monitors and automatic insulin pumps can track glucose levels and provide the right amount of insulin, making managing type 1 diabetes a little easier. Figuring out the right amount of insulin is important, because chronically elevated blood glucose levels can cause damage to tissues around the body. However, too much insulin will cause hypoglycemia, which can be very dangerous.

Type 1 diabetes is most commonly diagnosed in childhood, but it has been known to develop at any age. It's much less common than type 2 diabetes, accounting for 5-10% of cases of diabetes.

The following video, from the charity Diabetes UK, provides a nice review of type 1 diabetes: https://youtu.be/C3AQIfgthh4

Type 2 Diabetes:

Development of type 2 diabetes begins with a condition called insulin resistance. At least initially, the pancreas is producing enough insulin, but the body's cells don't respond appropriately. It's as if you still have the insulin key but can't find the keyhole to unlock the doors and let the glucose in.

Fig. 5.7. In type 2 diabetes, the cell does not respond appropriately to insulin, so glucose is stuck outside the cell.

The result is the same: high blood glucose. At this point, you may be diagnosed with a condition called prediabetes. The pancreas tries to compensate by making more insulin, but over time, it becomes exhausted and eventually produces less insulin, leading to full-blown type 2 diabetes. According to the CDC, 100 million Americans are living with diabetes (30.3 million) or prediabetes (84.1 million).

Although people of all shapes and sizes can get Type 2 diabetes, it is strongly associated with abdominal obesity. In the past, it was mainly diagnosed in older adults, but it is becoming more and more common in children and adolescents as well, as obesity has increased in all age groups. In the maps below, you can see that as obesity has increased in states around the country, so has diabetes.   

Fig. 5.8. Data from the CDC show the increasingly prevalence of both obesity and type 2 diabetes between 1994 and 2015.

The complications of type 2 diabetes result from long-term exposure to high blood glucose, or hyperglycemia. This causes damage to the heart, blood vessels, kidneys, eyes, and nerves, increasing the risk of heart disease and stroke, kidney failure, blindness, and nerve dysfunction. People with uncontrolled Type 2 diabetes can also end up with foot infections and ulcers because of impaired nerve function and wound healing. If left untreated, this results in amputation.

This video, also from Diabetes UK, reviews the causes, complications, and treatments for type 2 diabetes: https://youtu.be/4SZGM_E5cLI

The link between obesity and type 2 diabetes is explored in this video, part of the Weight of the Nation series by HBO: https://youtu.be/l5rYq-G1A5M

Gestational diabetes:

Gestational diabetes is diabetes that develops during pregnancy in women that did not previously have diabetes. It affects approximately 1 to 2 percent of pregnancies in the U.S. It can cause pregnancy complications, mostly associated with excess fetal growth because of high blood glucose. Although it usually goes away once the baby is born, women who have gestational diabetes are more likely to develop type 2 diabetes later in life, so it is a warning sign for them.

This video from Kahn Academy does a nice job of explaining the causes of the different types of diabetes: https://youtu.be/c9LwwQK5588

Diabetes Management:

All of the following have been shown to help manage diabetes and reduce complications. Diabetes management, as well as prevention (particularly if you've been diagnosed with prediabetes), starts with lifestyle choices.

• Exercise helps to improve your body's insulin response and can also help maintain a healthy weight.

• Eating well with diabetes doesn't require a special diet but instead regular, balanced meals following the Dietary Guidelines. It isn't necessary to eliminate carbohydrates or eat a low-carbohydrate diet, but emphasizing whole food sources of carbohydrate helps with blood glucose regulation.

• Managing stress levels and getting enough sleep can also help with blood glucose regulation.

• Medications may be needed. Insulin is needed for type 1 diabetes and may be needed for more advanced or severe cases of type 2 or gestational diabetes. Other medications can also help. If lifestyle choices aren't enough to manage diabetes, it is important to use medications appropriately to help reduce the complications of chronic high blood glucose.

Self Check

References

1. Salway, J.G., Metabolism at a Glance, Blackwell Publishing, 2004.

2. Smolin, L. and Grosvenor, M. 2016. Nutrition Science and Applications. John Wiley and Sons.

3. Gibson, A.A. et al. 2015. Do ketogenic diets really suppress appetite? A systematic review and meta-analysis, Obesity Reviews, 16(1):64-76, https://www.ncbi.nlm.nih.gov/pubmed/25402637

4. Hall, K.D. et al. 2016. Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. Am. J. Clin. Nutr. 104(2):324-33. https://www.ncbi.nlm.nih.gov/pubmed/27385608

5. Abassi, J. 2018. Interest in Ketogenic Diet Grows for Weight Loss and Type 2 Diabetes, JAMA 319(3):215-217. https://jamanetwork.com/journals/jama/article-abstract/2669724

6. Belluz, J. 2018. The Keto Diet, Explained. Vox.com, https://www.vox.com/science-and-health/2018/2/21/16965122/keto-diet-reset

7. CDC, Diabetes Basics, https://www.cdc.gov/diabetes/basics/index.html

Image Credits

1. Fig. 4.1. Mouse islet image by Jakob Suckale, Wikipedia, CC BY-SA 3.0

2. Fig. 4.2. Glucose/insulin patterns in 24-hours figure by Jakob Suckale and Michele Solimena, CC BY 3.0, https///commons.wikimedia.org/wiki/File/Suckale08_fig3_glucose_insulin_day.png.

3. Fig. 4.3. Insulin action figure by Meiquer, Wikipedia, CC BY-SA 3.0, with additions by Alice Callahan, CC BY-NC-SA 4.0

4. Fig. 4.4. Glucose metabolism figure by Alice Callahan, CC BY-NC-SA 4.0, with ATP star by Anastasia Latysheva from the Noun Project

5. Fig. 4.5. Gluconeogenesis and ketogenesis figure by Alice Callahan, CC BY-NC-SA 4.0, with brain by monstara and liver by maritacovarrubias, both from Open Clip Art, public domain

6. Figs. 4.6 and 4.7 by Brian Lindshield, from "Kansas State University Human Nutrition (FNDH 400) Flexbook" (2018). NPP eBooks. 19.

7. Fig. 4.8 from CDC, public domain, https://www.cdc.gov/diabetes/data/center/slides.html

Fiber - Types, Food Sources, Health Benefits, and Whole vs. Refined Grains

Dietary fiber is defined by the Institute of Medicine's Food and Nutrition Board as "nondigestible carbohydrates and lignin that are intrinsic and intact in plants." Fiber plays an important role in giving plants structure and protection, and it also plays an important role in the human diet.

Cellulose is one type of fiber. The chemical structure of cellulose is shown in the figure below, with our simplified depiction next to it. You can see that cellulose has long chains of glucose, similar to starch, but they're stacked up, and there are hydrogen bonds linking the stacks. The special bonds between these glucose units in fiber are not enzymatically digested in the digestive tract, and therefore, fiber passes undigested to the colon or large intestine.

Figure 6.1 - The chemical structure of cellulose, and a simplified illustration of cellulose.

You might be wondering how fiber has any benefit to us if we can't digest it. However, it doesn't just pass through the digestive tract as a waste product. Instead, it serves many functions on its journey, and these contribute to our health. Let's explore the different types of fiber, where we find them in foods, and what benefits they provide!

Types of Fiber

Whole plant foods contain many different types of molecules that fit within the definition of fiber. One of the ways that types of fiber are classified is by their solubility in water. Whole plant foods contain a mix of both soluble and insoluble fiber, but some are better sources of one than the other.

1. Soluble Fiber - These fibers dissolve in water, forming a viscous gel in the GI tract, which helps to slow digestion and the absorption of glucose. This means that including soluble fiber in a meal helps to prevent sharp blood sugar spikes, instead making for a more gradual rise in blood glucose. Consuming a diet high in soluble fiber can also help to lower blood cholesterol levels, because soluble fiber binds cholesterol and bile acids (which contain cholesterol) in the GI tract.  Soluble fiber is also highly fermentable, so it is easily digested by bacteria in the large intestine. Pectins and gums are common types of soluble fibers, and good food sources include oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. (Psyllium fiber supplements like Metamucil are composed mainly of soluble fiber, so if you've ever stirred a spoonful of this into a glass of water, you've seen the viscous consistency characteristic of soluble fiber.)

2. Insoluble Fiber - These fibers typically do not dissolve in water and are nonviscous. Some are fermentable by bacteria in the large intestine but to a lesser degree than soluble fibers. Insoluble fibers help prevent constipation, as they create a softer, bulkier stool that is easier to eliminate. Lignin, cellulose, and hemicellulose are common types of insoluble fibers, and food sources include wheat bran, vegetables, fruits, and whole grains.

Food Sources

Since fiber provides structure to plants, fiber can be found in all whole plant foods, including whole grains (like oatmeal, barley, rice and wheat), beans, nuts, seeds, and whole fruits and vegetables.

Figure 6.2 - A bowl of oatmeal topped with blueberries and sunflower seeds.

This meal is packed with fiber from the oatmeal, blueberries, and sunflower seeds.

When foods are refined, parts of the plant are removed, and during this process, fiber and other nutrients are lost. For example, fiber is lost when going from a whole fresh orange to orange juice. A whole orange contains about 3 grams of fiber, whereas a glass of orange juice has little to no fiber. Fiber is also lost when grains are refined. We will discuss this more a little later.

Take a look at the list of foods below to see the variety of foods which provide dietary fiber.

Table 6.1 Common foods listed with standard portion size, and calories and fiber in a standard portion.

Although you can get fiber from supplements, whole foods are are a better source, because the fiber comes packaged with other essential nutrients and phytonutrients.

Health Benefits of Dietary Fiber

A high-fiber diet has many benefits, which include:

• Helps prevent constipation. Many fibers (but mostly insoluble fibers) help provide a softer, bulkier stool which is then easier to eliminate.

• Helps maintain digestive and bowel health. Dietary fiber promotes digestive health through its role in supporting elimination and fermentation, and it's positive impact on gut microbiota. Since fiber provides a bulkier stool, this helps keeps the digestive tract muscles toned and strong which can help prevent hemorrhoids and diverticula.

• Lowers risk of cardiovascular disease. Higher fiber intake has been shown to improve blood lipids by reducing total cholesterol, triglycerides, and low density cholesterol ("bad cholesterol," associated with a higher risk of cardiovascular disease), and increasing high density cholesterol ("good cholesterol," associated with lower risk of cardiovascular disease). Higher fiber intake has also been associated with lower blood pressure and reduced inflammation.

• Lowers risk of type 2 Diabetes. Higher fiber intake (especially viscous, or soluble fibers) has been shown to slow down glucose digestion and absorption, benefiting glucose metabolism. A higher fiber diet may also decrease diabetes risk by reducing inflammation.

• Lowers risk of colorectal cancer. More evidence is supporting the idea that higher fiber intake lowers the risk of colorectal cancer, although researchers aren't sure why. One hypothesis is that dietary fiber decreases transit time (the time it takes for food to move through the digestive tract), thereby exposing the cells of the gastrointestinal tract to carcinogens from food for a shorter time.

• Helps maintain a healthy body weight. Research has shown a relationship between higher dietary fiber intake and lower body weight. The mechanisms for this are unclear, but perhaps high-fiber foods are more filling and therefore keep people satisfied longer with fewer calories. High-fiber foods also tend to be more nutrient-dense compared to many processed foods, which are more energy-dense.  

Whole vs. Refined Grains

Figure 6.3 - Wheat growing in a field.

Before they are harvested, all grains  are whole grains. They contain the entire seed (or kernel) of the plant. This seed is made up of three edible parts: the bran, the germ, and the endosperm. The seed is also covered by an inedible husk that protects the seed.

Figure 6.4 - The anatomy of a wheat kernel which includes the bran, endosperm, and germ.

1. The bran is the outer skin of the seed. It contains antioxidants, B vitamins and fiber.

2. The endosperm is by far the largest part of the seed and provides energy in the form of starch to support reproduction. It also contains protein and small amounts of vitamins and minerals.

3. The germ is the embryo of the seed -- the part that can sprout into a new plant. It contains B vitamins, protein, minerals like zinc and magnesium, and healthy fats.

The Dietary Guidelines for Americans define whole grains and refined grains in the following way:

"Whole Grains—Grains and grain products made from the entire grain seed, usually called the kernel, which consists of the bran, germ, and endosperm. If the kernel has been cracked, crushed, or flaked, it must retain the same relative proportions of bran, germ, and endosperm as the original grain in order to be called whole grain. Many, but not all, whole grains are also sources of dietary fiber."

Whole grains include foods like barley, corn (whole cornmeal and popcorn), oats (including oatmeal), rye, and wheat. (For a more complete list of whole grains, check out the Whole Grain Council.)

"Refined Grains—Grains and grain products with the bran and germ removed; any grain product that is not a whole-grain product. Many refined grains are low in fiber but enriched with thiamin, riboflavin, niacin, and iron, and fortified with folic acid."

Refined grains include foods like white rice and white flour. According to the Whole Grain Council, "Refining a grain removes about a quarter of the protein in a grain, and half to two thirds or more of a score of nutrients, leaving the grain a mere shadow of its original self."

Refined grains are often enriched with vitamins and minerals, meaning that some of the nutrients lost during the refining process are added back in after processing. However, many vitamins and minerals are not added back, and neither are the fiber, protein, and healthy fats found in whole grains. In the chart below you can see the differences in essential nutrients between whole wheat flour, refined wheat flour, and enriched wheat flour.

Figure 6.5 - The nutrient content of refined wheat and enriched wheat as compared to whole wheat flour.

Because whole grains offer greater nutrient density, MyPlate and the Dietary Guidelines recommend that at least half of our grains are whole grains. Yet current data show that while most Americans are eating enough grains overall, they're eating too many refined grains and not enough whole grains, as shown in this graphic from the Dietary Guidelines:

Figure 6.6 - Average Whole & Refined Grain Intakes in Ounce-Equivalents per Day by Age-Sex Groups, Compared to Ranges of Recommended Daily Intake for Whole Grains & Limits for Refined Grains.

Looking for whole grain products at the grocery store can be tricky, since the front-of-package labeling is about marketing and selling products. Words like "made with whole grain" and "multigrain" on the front of the package make it appear like a product is whole grain, when in fact there may be very few whole grains present.

The color of a bread can be deceiving too. Refined grain products can have added caramel color to make them appear more like whole grains.

To determine if a product is a good source of whole grain, the best place to look is the ingredient list on the Nutrition Facts panel. The ingredients should list a whole grain as the first ingredient (ex.100%  whole wheat), and it should not be followed by a bunch of refined grains (like enriched wheat flour).

Getting familiar with the name of whole grains will help you identify them. Common varieties include wheat, barley, brown rice, buckwheat, corn, rye, oats, and wild rice. Less known varieties are: teff, amaranth, millet, quinoa, black rice, black barley, and spelt.

Most, but not all, whole grains are a good source of fiber, and that is one of the benefits of choosing whole grains. Keep in mind that some products add extra fiber as a separate ingredient, like wheat bran, inulin, or cellulose. These boost the grams of fiber on the Nutrition Facts label and may make the product a good source of fiber, but it doesn't mean it's a good source of whole grains. In fact, it may be a product made mostly of refined grains, so it would still be missing the other nutrients that come packaged in whole grains and may not have the same health benefits.  Therefore, just looking at fiber on the Nutrition Facts label is not a good indicator of whether or not the product is made with whole grains.

Also, some products that are 100% whole wheat but do not appear to be a good source of fiber, because the serving size is small. The bread label below is an example of this. The first ingredient is "stone ground whole wheat flour" with no refined flours listed, but it still has only 2g of fiber and 9% DV. But of course, that still contributes to your fiber intake for the day, and if you made yourself a sandwich with two slices of bread, that would provide 18% of the DV.

Figure 6.7 - Example of 100% whole wheat bread with Nutrition Facts and ingredient list.

The following video gives more information on how to determine if products are 100% whole grain, "Label Reading and Whole Grains."

Self Check

References

1. Institute of Medicine, Food and Nutrition Board, 2005. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, DC; The National Academy of Sciences.

2. Source: U.S Department of Agriculture, Agricultural Research Service, Nutrient Data Laboratory. 2014. USDA National Nutrient Database for Standard Reference, Release 27. Available at: http://www.ars.usda.gov/nutrientdata.

3. Academy of Nutrition and Dietetics, 2015, Position of the Academy of Nutrition and Dietetics: Health Implications of Dietary Fiber, Journal of the Academy of Nutrition and Dietetics 115(11):1861–1870.

4. Whole Grain Council

5. Dietary Fiber: Essential for a healthy diet, Mayo Clinic, https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/fiber/art-20043983

Image Credits

1. Chemical structure of cellulose by laghi.l, CC BY-SA 3.0

2. Bowl of oatmeal image by Rusvaplauke, https://flic.kr/p/2zRGwE, CC BY-NC-ND 2.0.

3. Grain image by rethought, http://flic.kr./p/8maoBU, CC BY-NC 2.0

4. Wheat kernel image by Phuthinh Co, http://flic.kr/p/cz9w2b, CC BY-SA 2.0

5. Wheat kernel with nutrition image by Phuthinh Co, http://flic.kr/p/cAuBb5, CC BY-SA 2.0

6. Chart comparing nutrient content of whole wheat flour, refined flour and enriched wheat flour, "Oldways Whole Grains Council",  "www.wholegrainscouncil.org"

7. Whole grain intake graphic from Dietary Guidelines for Americans, Figure 2-5, https://health.gov/dietaryguidelines/2015/guidelines/chapter-2/a-closer-look-at-current-intakes-and-recommended-shifts/

8. 100% whole wheat bread and label photos by Tamberly Powell, CC BY-NC-SA 4.0

Sugar: Food Sources, Health Implications, Intakes, and Label-Reading to Identify Sugar

Food Sources of Naturally-Occurring and Added Sugars

As we've already discussed, sugars are naturally found in fruits, veggies, and dairy. These are nutrient dense foods that come packaged with other essential nutrients too.

Figure 7.1 Examples of food that contain naturally occuring sugars: fruit, vegetables, and dairy.

Fresh fruits and veggies contain naturally-occurring sugars like glucose, fructose, and sucrose, but also come packaged with fiber, potassium, and Vitamin C. Dairy foods like unsweetened yogurt, milk, and cheese contain naturally-occurring lactose but also come packaged with calcium, potassium, phosphorus, and riboflavin.

Another food that contains natural sugar in the form of maltose is sprouted grain bread. In the example below, the only ingredients are sprouted organic rye kernels and water, yet there are 7g of sugar per slice. This sugar must be naturally-occuring maltose, and as you can imagine, it comes packaged with nutrients like fiber, protein, and iron.

Figure 7.2 An example of a sprouted wheat bread that contains naturally occuring maltose from sprouted rye kernels.

In contrast, added sugars are concentrated sweeteners that are added as ingredients to foods to make them sweeter. They add calories to a food but contribute little to no essential nutrients, so they decrease the nutrient density of foods. Among the most common sources of added sugar are table sugar (sucrose) and high fructose corn syrup, but they come in many different forms with different names. For example, honey, maple syrup, agave nectar, and brown rice syrup may all sound more wholesome and natural, but they're still added sugars, because they are concentrated sweeteners that contribute little to no other nutrients. Other names for added sugar you might not recognize as sweeteners at all, like barley malt or treacle. Here's a list of 61 different names for added sugars:

Figure 7.3 - Names of sugar commonly added to food.

We find added sugars in some expected places, like cookies, ice cream, and soda, but there can also be a surprising amount of added sugar in yogurt, breakfast cereals, energy bars, and plant-based milk alternatives, like soy milk. We also find added sugars hiding in unexpected places, like ketchup, salad dressings, bread, and pasta sauce. In fact, nearly 75% of packaged products in the U.S. food supply are now sweetened.

In general, most people don't need to worry much about how much naturally-occurring sugar they consume. This goes back to the fact that naturally-occurring sugars are packaged with other nutrients. For example, a large apple contains about 23 grams of sugar, more than half of it in the form of fructose. However, it also has more than 5 grams of fiber, plus a significant amount of vitamin C and potassium. The fiber slows down the digestion and absorption of the sugar into your bloodstream, giving your body more time to metabolize it and giving you a greater feeling of fullness.

A single can of soda, on the other hand, contains about 33 grams of sugar. It's in a similar chemical form as the sugar in the apple -- a mix of fructose and glucose -- but it's not accompanied by any fiber to slow down digestion. Therefore, it's rapidly absorbed into your bloodstream, and your body has to quickly metabolize the fructose to glucose and increase insulin secretion to process the spike in sugar. Plus, although the soda contains 150 Calories and the apple has just 116, the apple is probably going to leave you feeling more satisfied and less hungry compared with the soda.

For all of these reasons, it's the added sugars that we worry about, not the naturally-occurring ones. That said, there is room for some added sugar in a balanced diet, and you can use it to make nutrient-dense food tastier. For example, you can drizzle honey into plain yogurt or sprinkle some brown sugar on roasted winter squash. You get far more nutritional "bang for your buck" using added sugars in this way than consuming them in something like a soda. (And of course, there's also room in a balanced diet for occasional treats!)

How much added sugar are we eating?

On average, Americans consume 22 to 30 teaspoons of added sugar daily, up to 17% of Calories, well in excess of the recommendation to limit added sugar intake to 10% of Calories or less. This is shown in the image below from the Dietary Guidelines.

Figure 7.4 - Average intakes of added sugars as a percent of calories per day by age-sex group, in comparison to the Dietary Guidelines' maximum limit of less than 10 percent of calories.

Where are all of these added sugars coming from? Nearly half of them come from soda, juices, and other sugary drinks, as illustrated below. Therefore, the Dietary Guidelines recommend that people drink more water and less sugary drinks.

Figure 7.5 - Food category sources of added sugars in the U.S. population ages 2 years and older.

On the Nutrition Facts panel, sugar is expressed in grams, but most of us don't think in grams. Therefore, it can be helpful to convert gram amounts to teaspoons, which are easier to visualize. Use the conversions shown in the graphic below to make these calculations.

Figure 7.6 - One teaspoon is equal to 4g of sugar or a sugar cube.

The sugar in soda adds up fast, especially with our super size portions. For example, a 64 oz. soda has 186 grams of sugar, or about 46 teaspoons. (186g divided by 4g/tsp = 46 tsp.)  

Figure 7.7 - Forty six sugar cubes stacked next to a big gulp to illustrate the 46 teaspoons of sugar that the soda contains.

It can be eye-opening to track your added sugar intake for a few days, and this may give you an idea of sources of added sugar that you can live without and replace with something else. However, tracking added sugar intake is difficult to do since it can be hard to differentiate added and naturally-occurring sugars on food labels. In the big picture, it's most important to focus on eating WHOLE foods that are minimally processed and to consume added sugars in moderation.

Benefits of Eating Less Added Sugar

Research shows that adopting an eating pattern that is relatively low in added sugars has many benefits, including a lower risk of:

• Cardiovascular disease

• Obesity

• Type 2 diabetes

• Some cancers

• Dental cavities

Why does too much added sugar cause health problems? The reasons are complex, and this is an ongoing area of research and controversy. One possible explanation is that a diet high in added sugar means the pancreas has to work hard to make enough insulin, and over time, it can begin to fail and the body's cells start to become insulin resistant. The liver also has to work hard to metabolize fructose, and too much fructose increases fat synthesis, which can raise blood lipid and cholesterol levels, increasing risk of heart disease.

Both dietary sucrose and starch are associated with tooth decay. Bacteria living in the mouth can utilize the carbohydrates passing through the oral cavity for their own benefit. Those bacteria happily metabolize carbohydrates, especially sucrose, but also starchy foods, which stick to teeth and linger there. Acid is formed in the process, and this can dissolve your tooth enamel, eventually causing cavities, also known as dental caries. Reducing sugar intake, limiting between-meal snacks, and brushing after meals to remove lingering carbohydrates can help reduce the risk of dental caries. The use of fluoride and regular dental care also help.

Fig. 7.8. Dental caries are formed because of a combination of factors: the presence of oral bacteria; a supply of sugar and/or starch for them to eat; tooth surface where they can form colonies, or plaque; and time.

Are Some Added Sugars Better Than Others?

Students often ask which sugar is healthiest: high fructose corn syrup, honey, agave syrup, or sugar? In general, as far as the body is concerned, sugar is sugar. These are all concentrated sweeteners that contain Calories with very few/no other nutrients, so all should be used only in moderation.  

High fructose corn syrup (HFCS) has gotten a lot of attention in the last several decades and has been blamed for the obesity epidemic and many other poor health outcomes. This is in part because it's widely used to sweeten soda and so has become a large part of the American diet. It's true that fructose is more work for the body to process, because it has to be converted to glucose. Here's what the website Sugar Science, written by researchers and scientists from the University of California, San Francisco, has to say about the difference between table sugar and high fructose corn syrup:

"Table sugar (sucrose), derived from sugar cane and beets, is made up of equal portions of two types of sugars. It's half (50%) glucose and half (50%) fructose. High-fructose corn syrup (HFCS) is derived from corn syrups that have undergone enzymatic processing to convert some of their glucose into fructose to produce a desired sweetness. HFCS comes in different formulations, depending on the manufacturer.  More common formulations contain 42% fructose or 55% percent, but some contain as much as 90%. Why should we care? First, because there is significant evidence that fructose is processed differently in the body than other sugars and can be toxic to the liver, just like alcohol. Second, because as a nation, we have been consuming more of our sugars in HFCS over time."

But focusing too much attention on fructose as the problem may risk missing the forest for the trees. Here's what Dr. Luc Tappy, a fructose researcher at University of Lausanne, had to say about the issue in an article on Vox.com:

"Given the substantial consumption of fructose in our diet, mainly from sweetened beverages, sweet snacks, and cereal products with added sugar, and the fact that fructose is an entirely dispensable nutrient, it appears sound to limit consumption of sugar as part of any weight loss program and in individuals at high risk of developing metabolic diseases. There is no evidence, however, that fructose is the sole, or even the main factor in the development of these diseases, nor that it is deleterious to everybody, and public health initiatives should therefore broadly focus on the promotion of healthy lifestyles generally, with restriction of both sugar and saturated fat intakes, and consumption of whole grains, fresh fruits and vegetables rather than focusing exclusively on reduction of sugar intake."

The following video, produced by the American Chemical Society, gives more information about HFCS and sugar, "Explained: The actual difference between sugar and high-fructose corn syrup".

Are sweeteners such as honey, maple syrup, and molasses any better than more refined and processed sweeteners? Maybe. These sweeteners do contain minerals and antioxidants, so they may offer a slight edge in terms of nutrition. However, keep in mind that minerals and antioxidants are abundant in whole foods such as whole grains, vegetables, and fruits, and these obviously offer many other benefits. These sweeteners are still considered sources of added sugar and should be used in moderation. That said, each of them offers different delicious flavors, and honey has the added benefit that it can be purchased locally, so there are good reasons to turn towards these products when you want to add some sweetness to your food.

Label-Reading to Identify Sugar

If you're trying to figure out if a food is high in sugar, there are two places you should look on the label. First, check the Nutrition Facts panel to see how many grams of sugar are in one serving. However, labels are not yet required to list added sugars separately (though some are doing this already), so be aware that the "Sugars" on the label includes both added and naturally-occurring sugars. That's why you also need to check the ingredients list to look for any sources of added sugar (may be listed as any of the 61 different names in the graphic high on this page.)

Let's take a look at some labels to practice identifying natural and added sugars in foods.  

Below are labels from an 8-ounce serving of Plain Yogurt. There are 12 grams of sugar listed on the label. Is this sugar naturally-occurring or added?

Figure 7.9 - Plain yogurt with Nutrition Facts and ingredient list.

To answer this question, look at the ingredients. They include nonfat milk, maltodextrin (a food additive that is a polysaccharide), milk protein concentrate, vitamins and bacteria. There are no sources of added sugar in the ingredient list, so the 12 grams of sugar shown on the Nutrition Facts are from naturally-occurring lactose in the milk.

Next, look at the label below for an 8-ounce serving of sweetened strawberry yogurt. There are 35 grams of sugar listed on the label. Is this sugar naturally-occurring or added?

Figure 7.10 - Strawberry yogurt with Nutrition Facts and ingredient list.

To answer this question, we again have to look at the ingredients list. Like the plain yogurt, the first ingredient is milk, but this strawberry yogurt also contains cane sugar and strawberries. Based on these ingredients, the 35 grams of sugar are a combination of both added and naturally-occurring sugars. The added sugar comes from cane sugar, and the naturally-occurring sugar is from the lactose from the milk and the glucose, fructose and sucrose in the strawberries.

How much sugar is naturally-occurring and how much is added? To answer this, you have to do some detective work and compare the plain and sweetened yogurts. The strawberry yogurt has 23 more grams of sugar than the plain yogurt, but some of this is naturally-occurring from the strawberries, so we can't calculate this precisely. I bet a lot of this 23 grams of sugar is added since cane sugar is the second ingredient listed (maybe as much as 5 teaspoons). Once all food labels are updated to include added sugars, it will be easy to identify them on the Nutrition Facts.

Not all yogurts are created equal, and many of them have less ingredients and less sugar than the example given above with the Greek yogurt. One example is siggi's Icelandic style skyr. As you can see in the images below, the ingredients are simple, and there is a lot less sugar than traditional yogurts.

Figure 7.11 - Siggi's plain yogurt and Nutrition Facts.

In this Plain yogurt, a 5.3 oz serving has 16g of protein, and only 4g of naturally occurring lactose coming from milk. The only ingredients are milk and live active cultures.

Figure 7.12 - Siggi's strawberry yogurt and Nutrition Facts.

In the strawberry yogurt, a 5.3 oz serving has 11g of sugar. This would be a combination of naturally occurring sugars coming from the milk and strawberries, and added sugar coming from the cane sugar. The strawberry yogurt has 7g more sugar, than the plain yogurt, but some of this is coming from the strawberries. How much of this 7g of sugar is added? It is hard to know, but with cane sugar being one of the last ingredients, it may have only 1 teaspoon of added sugar (about 4g). This is a big difference from the strawberry Greek yogurt above.

Self Check

References

1. US Department of Health and Human Services and U.S. Department of Agriculture. 2015. Dietary Guidelines for Americans.

2. Institute of Medicine, Food and Nutrition Board, 2005. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, DC; The National Academy of Sciences.

3. Ng, S.W., Slining, M.M., & Popkin, B.M. (2012). Use of caloric and noncaloric sweeteners in US consumer packaged foods, 2005-2009. Journal of the Academy of Nutrition and Dietetics , 112(11), 1828-1834.e1821-1826.

4. Nutrition information for apple and soda: US Department of Agriculture, Agricultural Research Service, Nutrient Data Laboratory. USDA National Nutrient Database for Standard Reference, Legacy. Version Current:  April 2018. /nea/bhnrc/ndl, accessed September 12, 2018.

5. Belluz and Zarracina, "Sugar, explained", Vox. December 24, 2017. https://www.vox.com/science-and-health/2017/1/13/14219606/sugar-intake-dietary-nutrition-science

6. Sugar Science, "Too Much Can Make Us Sick," University of California, San Franciso, http://sugarscience.ucsf.edu/too-much-can-make-us-sick/#.W5lUKy-ZP-Y, accessed September 12, 2018.

7. Whitaker, E.M., "The Sweet Science of Honey," Sugar Science, UCSF, http://sugarscience.ucsf.edu/the-sweet-science-behind-honey.html#.W5qtp1InYdU, accessed September 13, 2018.

8. Phillips, K.M., et al., 2009, "Total antioxidant content of alternatives to refined sugar," J Am Diet Assoc., 109(1):64-71. https://www.ncbi.nlm.nih.gov/pubmed/19103324

Image Credits

1. 61 Names for Added Sugar graphic by Alice Callahan, CC BY-NC-SA 4.0. Source for list of sugars: SugarScience, "Hidden in Plain Sight," University of California, San Franscisco, http://sugarscience.ucsf.edu/hidden-in-plain-sight/#.W5li71Inbq0, accessed September 12, 2018.

2. Sprouted bread and label images by Tamberly Powell, CC BY-NC-S 4.0

3. Added sugar intake graphics from Dietary Guidelines for Americans, Figures 2-9 and 2-10, https://health.gov/dietaryguidelines/2015/guidelines/chapter-2/a-closer-look-at-current-intakes-and-recommended-shifts/

4. Sugar conversion graphic (Fig. 7.6) by Alice Callahan, CC BY-NC-SA 4.0. Includes sugar cube by jhnri4 and measuring spoon by mazeo at openclipart.org, public domain.

5. Dental caries graphic (Fig. 7.8) by Alice Callahan, CC BY-NC-SA 4.0. Includes photo of cavity by Suyash.dwivedi, CC BY-SA 4.0, https://commons.wikimedia.org/wiki/File:Dental_Caries_Cavity_2.JPG  

6. Yogurt and label images by Tamberly Powell, CC BY-NC-SA 4.0

Sugar Substitutes

You should now understand the problems with consuming too much added sugar, but what if you've sworn off regular soda and switched to diet versions? What if you're choosing "sugar-free" products, sweetened not with sugar but with sugar substitutes like aspartame, saccharin, or stevia? Are these a better choice?

Fig. 8.1 - Examples of products containing high-intensity sweeteners: diet soda, sugar-free chocolate, and bulk containers of Splenda and stevia extract.

Diet sodas are the biggest source of sugar substitutes in the American diet, but these ingredients are found in a range of foods, including ice cream, yogurt, cereals, iced tea, energy drinks, candy, cookies, granola bars, salad dressings, frozen dinners, and energy bars. Products containing sugar substitutes are often labeled as sugar-free or "lite," but some don't have any front-of-package labeling with this information, and you may not even realize that you're consuming them. With more consumers watching their sugar intake, the use of sugar substitutes is growing, and the food industry is working hard to market them as a healthier choice. We can expect to see them in more and more products, so it's important to understand what these substances are and what they may mean for our health.

What Are Sugar Substitutes?

You may find sugar substitutes called lots of different things, including artificial, non-nutritive, high-intensity, or low-calorie sweeteners. Regardless of the name, these are substances that have a sweet taste but few or no calories. In fact, they are much sweeter than sucrose, so a tiny amount can add a lot of sweetness to food. (Sweetener packets like Splenda and Equal contain a small amount of sweetener and a lot of filler ingredients.)

Table 8.1. Sugar substitutes approved by the FDA for use in the United States with their brand names and sweetness relative to sucrose.

Unlike regular sugar, the sweeteners listed in the table above are not associated with dental caries, and they don't raise blood glucose.

It turns out that the ice cream aisle is full of sugar substitutes! Can you spot the sugar substitutes in these "no sugar added" popsicles?

Correct. The sugar substitutes, sorbitol, acesulfame potassium, and sucralose are all listed in the ingredient list.

Sugar alcohols are another type of sugar substitute. They include sorbitol, mannitol, lactitol, erythritol, and xylitol. They are chemically similar to monosaccharides but different enough that they aren't processed in the body to the same extent. However, they are at least partially metabolized and contain about 2 kcal/gram (compared with 4 kcal/gram for sucrose). (An exception is erythritol, which contains just 0.2 kcal/g.) Unlike the sweeteners listed in the table above, they are not "high-intensity" but instead are generally less sweet than sucrose. Because they are not fully digested, consuming large amounts of them can cause bloating, gas, and diarrhea.

Sugar alcohols are often used in sugar-free chewing gums and breath mints and can carry a health claim that they don't promote tooth decay, because mouth bacteria can't easily metabolize them. Xylitol in particular has been studied for its ability to decrease the incidence of tooth decay. However, these studies generally use large doses. For example, a person might have to chew xylitol gum five times per day to see a benefit. The American Academy of Pediatric Dentistry supports the use of xylitol but says the evidence for benefit is not clear and that amounts required may not be practical in real life.

Can Sugar Substitutes Help With Weight Loss?

When people choose diet soda or a sugar-free dessert, they're probably assuming that it's a healthier choice and perhaps that it could help them lose weight. However, studies show this isn't necessarily the case.

In the short-term, if someone who drinks a lot of sugar-sweetened beverages switches to diet versions, studies show that this can result in weight loss. That makes sense, because you're removing a lot of empty calories from the diet.

However, in the long-term, studies show there isn't a clear benefit to consuming sugar substitutes. A recent systematic review and meta-analysis combined the results of studies that lasted at least 6 months. Among the randomized controlled trials, they found no difference in body mass index (BMI - a measure of the ratio of body weight to height) between people who consumed sugar and those who consumed sugar substitutes. Observational studies that tracked large groups over years found that people who consumed sugar substitutes tended to have a higher BMI, greater weight and waist circumference, and a higher incidence of obesity, hypertension, metabolic syndrome, type 2 diabetes, and cardiovascular events. Because these are observational studies, we can't conclude that the sugar substitutes cause these health outcomes, but we can conclude that their use is not associated with better health.

When it comes to weight management, the goal is to adopt eating habits that support a sustainable healthy body weight. Sugar substitutes might help in the short-term with decreasing calorie intake and perhaps gradually moving away from sweetened beverages, but better long-term goals for health would be to shift to water and other unsweetened beverages. If you're looking for a way to sweeten your oatmeal or yogurt, you might try adding fresh fruit rather than sugar or an artificial sweetener packet. (Or go ahead and add a bit of brown sugar or a drizzle of honey, keeping in mind the overall goal of moderation.)

Are High-Intensity Sweeteners Safe?

Over the years, there have been a number of concerns about non-nutritive sweeteners. For example, in the 1970s, studies showed that saccharin was linked to bladder cancer in lab rats, so it was labeled as a potential carcinogen, although its use as a sweetener continued. In 2000, after many studies showed no link between cancer and saccharin, the warning labels were no longer required. Some studies have also raised concerns about a link between aspartame and sucralose and cancer, but the FDA has reviewed this evidence and concluded: "Based on the available scientific evidence, the agency has concluded that the high-intensity sweeteners approved by FDA are safe for the general population under certain conditions of use." The National Cancer Institute also says there is no clear evidence that high intensity sweeteners cause cancer.

Fig. 8.2 - A "Saccharin Notice" sign warns consumers that a grocery store shelf contains products with saccharin, which has been shown to cause cancer in laboratory animals. Between 1977 and 2000, products containing saccharin had to include a cancer warning label. This requirement was removed after the U.S. Department of Health and Human Services determined it was not a concern in humans at doses typically consumed.

There are other emerging safety concerns about sugar substitutes, though. Small studies on both mice and humans show that consuming artificial sweeteners can change our gut bacteria and cause glucose intolerance. Glucose intolerance means that blood glucose is abnormally elevated, showing that glucose metabolism is not working properly, and it is a precursor to the development of diabetes. Other researchers worry that having the taste of sweetness signaled to the brain without accompanying calories could derail our normal pathways for sensing hunger and satiety and for regulating glucose metabolism. This research is alarming but still preliminary. However, it is an active area of study, and we can expect more information to emerge in the years to come.

Are Natural Sweeteners Better Than Artificial Ones?

Sweeteners made from the stevia plant and from monk fruit extracts are both derived from plants and so are considered more natural than the other choices. However, it's important to not confuse natural with safe. Remember that many things in nature are dangerous, even deadly. (Consider cyanide, poisonous mushrooms, and botulinum toxin, for example.) Stevia sweeteners, which are growing in popularity and are often marketed as a more natural alternative, are made through a highly industrial extraction process, and some are produced by genetically-modified yeast. None of that makes them inherently less safe, but it does highlight that they aren't exactly natural.

Fig. 8.3 - A box of Sweetleaf sweetener, marketed as "Natural Stevia Sweetener."

What's important is how well these products are tested and studied for their safety. The Center for Science in the Public Interest, a consumer advocacy nonprofit organization, has criticized the FDA for not requiring more testing of stevia and monk fruit extracts, although they recommend stevia as one of the safer options for sugar substitutes based on existing data. However, recent research has shown that, like artificial sweeteners, stevia also affects the growth of gut bacteria.

What's the Bottom Line?

Sugar substitutes can add sweetness to a food without the calories, and they aren't associated with tooth decay. Despite concerns over the years, they probably don't cause cancer. However, they may not help with weight loss or maintenance in the long-term, and recent research shows that they may alter the gut microbiota and metabolic health.

Self Check

References

1. American Academy of Pediatric Dentistry. 2015. "Policy on the Use of Xylitol."

2. Azad, Meghan B., Ahmed M. Abou-Setta, Bhupendrasinh F. Chauhan, Rasheda Rabbani, Justin Lys, Leslie Copstein, Amrinder Mann, et al. 2017. "Nonnutritive Sweeteners and Cardiometabolic Health: A Systematic Review and Meta-Analysis of Randomized Controlled Trials and Prospective Cohort Studies." CMAJ 189 (28): E929–39. https://doi.org/10.1503/cmaj.161390.

3. Callahan, Alice. 2018. "Are There Downsides to the Sweetener Stevia?" The New York Times, June 9, 2018, sec. Well. https://www.nytimes.com/2018/05/04/well/eat/stevia-sweetener-sugar-side-effects-downsides.html.

4. Center for Science in the Public Interest. 2015. "Sweet Nothings: Safe... or Scary? The Inside Scoop on Sugar Substitutes."

5. Food and Drug Administration. "Food Additives & Ingredients - Additional Information about High-Intensity Sweeteners Permitted for Use in Food in the United States." Accessed September 20, 2018a. https://www.fda.gov/Food/IngredientsPackagingLabeling/FoodAdditivesIngredients/ucm397725.htm.

6. Food and Drug Administration. "Food Additives & Ingredients - High-Intensity Sweeteners." WebContent. Accessed September 20, 2018b. https://www.fda.gov/Food/IngredientsPackagingLabeling/FoodAdditivesIngredients/ucm397716.htm.

7. National Cancer Institute. 2005. "Artificial Sweeteners and Cancer." August 18, 2005. https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/artificial-sweeteners-fact-sheet.

8. Pearlman, Michelle, Jon Obert, and Lisa Casey. 2017. "The Association Between Artificial Sweeteners and Obesity." Current Gastroenterology Reports 19 (12): 64. https://doi.org/10.1007/s11894-017-0602-9.

9. Pepino, M. Yanina. 2015. "Metabolic Effects of Non-Nutritive Sweeteners." Physiology & Behavior 152 (0 0): 450–55. https://doi.org/10.1016/j.physbeh.2015.06.024.

10. Ruyter, Janne C. de, Margreet R. Olthof, Jacob C. Seidell, and Martijn B. Katan. 2012. "A Trial of Sugar-Free or Sugar-Sweetened Beverages and Body Weight in Children." New England Journal of Medicine 367 (15): 1397–1406. https://doi.org/10.1056/NEJMoa1203034.

11. Shell, Ellen Ruppel. n.d. "Artificial Sweeteners May Change Our Gut Bacteria in Dangerous Ways." Scientific American. Accessed September 20, 2018. https://doi.org/10.1038/scientificamerican0415-32.

12. Suez, Jotham, Tal Korem, David Zeevi, Gili Zilberman-Schapira, Christoph A. Thaiss, Ori Maza, David Israeli, et al. 2014. "Artificial Sweeteners Induce Glucose Intolerance by Altering the Gut Microbiota." Nature 514 (7521): 181–86. https://doi.org/10.1038/nature13793.

13. Wang, Qiao-Ping, Duncan Browman, Herbert Herzog, and G. Gregory Neely. 2018. "Non-Nutritive Sweeteners Possess a Bacteriostatic Effect and Alter Gut Microbiota in Mice." PLoS ONE 13 (7). https://doi.org/10.1371/journal.pone.0199080.

Image Credits

1. Diet Hansen's can by 7 Bits of Truth, CC BY 2.0, https://flic.kr/p/3g5uS

2. Sugar-free chocolate by m01229, CC BY 2.0, https://flic.kr/p/hANmCq

3. Sweeteners photo by sriram bala, CC BY-NC 2.0, https://flic.kr/p/3N9UY7

4. Saccharin notice photo by Linda Bartlett, National Cancer Institute, Public Domain

5. Stevia photo by Mike Mozart, CC BY 2.0, https///flic.kr/p/qFqMS7